The purpose of this paper is to identify some variations among experimental programs and discuss the manner in which such variations seem to affect a program's success. To accomplish this purpose an in-depth analysis of a few major preschool intervention studies is made in terms of four pertinent variables: (1) Curriculum Model (2) Home Intervention (3) Age at Intervention and (4) Duration of Intervention. The Westinghouse Report evaluating the impact of Head Start, the Gray and Klaus program, the Indiana Project, the Karnes program, the Weikart program, Montessori, and the Bereiter-Engelmann program are compared. A few general observations and tentative speculations are made about several other variables which appear to affect the outcome of preschool interventions. The evaluation of preschool outcomes might involve the four major variables in determining what modifications would improve preschool intervention results with disadvantaged children. (WY)